Pteronotus parnellii and Rhinolophus ferrumequinum utilize a Doppler shift type of sonar, that is they lower their pulse frequencies so that the echo frequencies remain constant. Studies are being carried out on both species using a pendulum device to monitor echolocative behavior under simulated flight conditions. Both species accurately Doppler shift compensate during acceleration and deceleration phases of the pendulum swing; neither compensate for negative shifts during the backward swing. Further experiments will be carried out in order to directly compare and/or contrast the sonar systems of these two species. In addition, anatomical studies using the LM, TEM, and SEM are continuing on the cochleae of Rhinolophus and Pteronotus in order to compare structures of the inner ear. Results to date indicate the evolution of very different specializations. Work will also continue on quantitative comparisons of nerve fibers in the sparsely and densely innervated regions, and the unusual lining of the scala tympani will be further examined with TEM and X-ray microanalysis. Frequency mapping after acoustic overstimulation will be completed.